1. Field of the Invention
The present invention is broadly concerned with methods and compositions for protecting plants from bacterial diseases. More particularly, the inventive compositions comprise an aqueous solution of saponins. These compositions are directly applied to seeds, seedlings, shoots, foliage, etc. of the plant to be protected. In addition to bacterial diseases, the compositions are useful for protecting the plants against fungal and viral diseases.
2. Description of the Prior Art
There are numerous diseases which may harm or even kill plants. Fungal diseases are one such type of disease. For example, Rhizoctonia solani (Rhizoctonia Canker, Black Scurf, or Helminthosporium solani (Silver Scurf)) and Phytophthora infestans (Late Blight) are both fungal diseases which are extremely dangerous to potato crops. In rhizoctonia infections, sclerotia or mycelium invade emerging sprouts, potato stems, roots, and stolons after germination occurring in early spring. On mature tubers or potatoes, the disease appears as black hard bodies known as Black Scurf with the tuber skin underneath often remaining unharmed. The disease leads to a delay in the emergence of the sprouts and stems, and causes the sprouts and stems to have a reddish canker girdling them when they finally do emerge.
The symptoms of late blight first appear on older leaves soon after flowering of the plant. The leaves turn dark brown and brittle, while the tuber exhibits lesions which often appear around the eyes. Furthermore, the infected portions of the tuber are granular in nature and penetrate as much as 2 cm into the tuber. All of these symptoms cooperate to reduce tuber yields and quality.
Both rhizoctonia and late blight readily infect potato plants and require extreme measures to avoid or minimize transmission thereof. For example, crop rotation is commonly practiced in an attempt to avoid diseased crops. Additionally, growers often seek seeds that are certified as being disease-free. However, these and other currently available measures do not adequately protect against the diseases. There is a need for preventive treatments that will protect potatoes and other plants from these and other harmful diseases.
Bacterial diseases also pose significant problems to plants, especially, tomatoes. Such bacterial diseases include bacterial spot (caused by Xanthomonas campestris pv. vesicatoria) and target spot (caused by Corynesporia cassiicola). A number of bactericide compositions are presently available for combating these bacterial diseases. KOCIDE, available from Griffin, L. L. C., Valdosta, Ga., is a leading bactericide which utilizes copper as the primary antibacterial agent. However, due to the prolonged use of copper antibacterial agents, bacteria are showing signs of increased resistance to copper, thereby reducing the effectiveness of the bactericide in controlling disease. Furthermore, agricultural runoff from these agents is finding its way into coastal waters and potentially causing harm to various marine life, especially shrimp and other invertebrates.
Because of the problem of bacteria developing resistance to various antibacterial compositions, attempts have been made to develop compositions which stimulate the plant""s own defense genes to cause the plant to produce proteins which inhibit disease. These products produce what is commonly known as a systemic activated resistance (SAR) response within the plant. ACTIGARD, available from Syngenta, Wilmington, Del., is one such product designed to stimulate a systemic response within the plant to combat the bacteria. ACTIGARD contains the active ingredient acibenzolar-s-methyl. While reasonably effective in controlling bacterial disease, it is a relatively expensive treatment option for farmers. Therefore, there is a need for an economical method for stimulating a plant""s own immune system to combat bacterial diseases, preferably employing a naturally derived composition in order to lessen potential environmental concerns.
Quinoa is classified as a member of the Chenopodiaceae, a large and varied family which includes cultivated spinach and sugar beet. Quinoa is an extremely hardy and drought-resistant plant which can be grown under harsh ecological conditionsxe2x80x94high altitudes, relatively poor soils, low rainfall, and cold temperaturesxe2x80x94that other major cereal grains, such as corn and wheat, cannot tolerate.
Quinoa originated in the Andes region of South America where it was a staple grain in pre-Spanish Conquest times. Traditional uses of quinoa declined after the Spanish Conquest. Cultivation and use of the grain was not widespread until a recent revival due to Western interest in this crop as a high lysine, high protein grain for human consumption. The principal obstacle to even wider human consumption of quinoa has been, and continues to be, the bitter taste of the saponin present in the grain.
Saponins are a type of sterol glycoside widely distributed in quinoa as well as other plants. There are generally two types of saponinxe2x80x94triterpene saponins and steroidal saponins. Traditionally, saponin has been removed by washing the grain in running water, although new methods have been developed recently (see, e.g., WO 99/53933).
Attempts have been made to utilize saponin as a synergist for other compounds which are useful for controlling the growth of pathogens (e.g., fungi) on plants. For example, U.S. Pat. No. 5,639,794 to Emerson et al., is directed towards a method for treating agricultural crops comprising the step of applying a so-called xe2x80x9cnatural productxe2x80x9d in combination with at least one saponin to kill, retard growth of, or displace pathogenic organisms. The natural products combined with the saponin are the various aldehydes, and particularly aromatic aldehydes, and the saponins are used to enhance the activity of the aldehyde (i.e., as a synergist). However, the use of aldehydes increases the cost of treating the plants and, in many instances, may be undesirable to the grower due to environmental concerns as well as the extra effort involved in handling these aldehydes.
There is a need for a cost-effective, environmentally friendly composition for effectively treating and/or preventing diseases in plants.
The instant invention overcomes the problems of the prior art by broadly providing effective compositions and methods for treating and/or protecting plants from diseases, especially bacterial disease.
In more detail, the Inventive compositions comprise (and preferably consist essentially of) saponins which act as a protectant for the plant independent of other compounds or agents (i.e., saponin is the principal and/or only active ingredient). As used herein, xe2x80x9cplantxe2x80x9d is intended to refer to any part of a plant (e.g., roots, foliage, shoot) as well as trees, shrubbery flowers, and grasses. xe2x80x9cSeedxe2x80x9d is intended to include seeds, tubers, tuber pieces, bulbs, etc., or parts thereof from which a plant is grown.
While any saponin is suitable for use in the compositions, the saponin should be derived from a plant different than the plant that the final saponin composition is intended to protect. Suitable sources of saponins include Quinoa, Quillaja, Primula (Primulae sp.), Senega (Polyga senega), Gypsophila, Horse chestnut (Aesculus sp.), Ginseng (Panax sp. and Eleutherocosus sp.), Licorice (Glycyrrhiza sp.). Ivy (Hedera sp.), Tea seed (Camellia cinensis), Alfalfa (Medicago sativa), Soya, Yucca (Yucca sp.), and Dioscorea. It is particularly preferred that the saponin be of the triterpene variety as found in quinoa and quillaja versus the steroidal types found in yucca.
A preferred method of extracting saponins from quinoa comprises placing a saponin-containing portion of a quinoa plant in an aqueous alcohol (e.g., methanol, ethanol) solution to form a saponin-containing solution and an extracted, solid residue. The alcohol is then removed from the solution followed by evaporation of the water to yield the saponin-containing product. Those skilled in the art will appreciate that the saponins can also be extracted from quinoa by other methods for use in the instant invention.
The saponin extract is preferably mixed with water to form the protective composition. If desired, the saponin extract can be mixed with water under mild heat (e.g., from about 10-35 E C) in order to effect mixing. Alternately, the saponin extract can be applied as a dry composition alone, or blended with a suitable carrier. Preferably, the composition comprises from about 25-300 g of saponin extract, and more preferably from about 50-200 g of saponin extract, per 100 liters of water, where the saponin extract has a triterpene saponin concentration of from about 10-70% by weight, and preferably at least about 50% by weight, based upon the total weight of the saponin extract taken as 100% by weight. Alternately, the saponins of the invention can be applied in a dry formulation using talc or some other particulate carrier. In such cases, the saponin component should be present at a level of from about 8-46% by weight, more preferably from about 16-36% by weight.
In use, plants or seeds are treated with the inventive compositions by simply contacting one or more portions of a diseased plant or seed, or a plant or seed susceptible to attack by disease, with a disease-inhibiting or protective amount of the composition so as to elicit a protective response in the plant or seed. This can be accomplished by spraying the plant or seed as well as by submerging it in the aqueous composition. Those skilled in the art will appreciate that portions of a plant can be selectively treated (e.g., infected leaves can be treated individually or the roots alone can be treated). Additionally, the seeds or tubers can be submerged in the aqueous composition and then planted and allowed to grow into a protected plant. Furthermore, the soil around the plant or seed can be treated as well. When the plant to be treated is a tree, the composition is preferably introduced into the vascular system of the tree by conventional methods. In a similar way, the dry saponin compositions can be applied by dusting or coating a plant part or seed.
It has also been found that the saponin products of the invention, and particularly the liquid versions thereof, are effective as foliar sprays. Such sprays would normally contain concentrations of saponin of from about 1 g/10 L to 150 g/10 L, and more preferably from about 10 g/10 L to 100 g/10 L.
Preferably, the plant or seed is not pre-treated with some other type of pathogen-controlling agent. Furthermore, it is preferred that the plant or seed is not treated with another pathogen-controlling agent simultaneous to treatment with the inventive composition. More specifically, it is preferred that the plants, seeds, or soils surrounding the plants have not been treated with some type of aldehyde composition. Thus, the plant and plant surfaces or the seed and seed surfaces should be essentially aldehyde-free (e.g., less than about 1 mg of aldehyde groups, per square centimeter of plant surface area to be treated) prior to treatment according to the invention.
Virtually any plant can be treated to prevent or lessen most plant diseases. For example, potato plants, tomato plants, sugar beets, canola, strawberries, chick peas, lentils, broccoli, cabbage, cauliflower, turf grass, tobacco, spinach, carrots, ginseng, radish, and field peas or seeds of any of the foregoing can all be protected with the inventive compositions. Furthermore, the compositions can be used to treat, control and/or prevent fungal diseases (e.g., rhizoctonia, late blight), Aphanomyces, Cercospora, Rhizopus, Sclerotium, ergot, Ascochyta, Fusarium, Anthracnose, Botrytis, and Ophiostoma (ceratocystis) ulmi (Dutch Elm disease). Plants or seeds treated according to the invention will remain essentially free of symptoms of the disease for at least about 20 days, preferably at least about 60 days, and more preferably at least about 100 days, after treatment. Thus, plants treated according to the invention, or plants grown from seeds treated according to the invention, will at least exhibit reduced levels of the disease compared to nontreated crops, and preferably will remain essentially free of symptoms of the disease throughout the natural growing season of the plant.